import { Factory } from './Factory'
import { Collection } from '../../util'
import {DependencyKey, DependencyRequirement, PropertyDependency} from '../types'

/**
 * Container factory which returns its token as its value, without attempting
 * to instantiate anything. This is used to register already-produced-singletons
 * with the container.
 *
 * @example
 * ```typescript
 * class A {}
 * const exactlyThisInstanceOfA = new A()
 *
 * const fact = new SingletonFactory(A, a)
 *
 * fact.produce([], [])  // => exactlyThisInstanceOfA
 * ```
 *
 * @extends Factory
 */
export default class SingletonFactory<T> extends Factory<T> {
    constructor(
        /**
         * Token identifying this singleton.
         */
        protected token: DependencyKey,

        /**
         * The value of this singleton.
         */
        protected value: T,
    ) {
        super(token)
    }

    produce(): T {
        return this.value
    }

    getDependencyKeys(): Collection<DependencyRequirement> {
        return new Collection<DependencyRequirement>()
    }

    getInjectedProperties(): Collection<PropertyDependency> {
        return new Collection<PropertyDependency>()
    }
}